1. Field of the Invention
This invention relates to the solvothermal synthesis of yttrium aluminium garnet (YAG). Specifically, this invention relates to a cost effective and novel means of producing high yields of nano-sized (<30 nm) YAG particles via a solvothermal synthesis process.
2. Description of the Related Art
Yttrium aluminum garnet (Y3Al5O12), or YAG, has many potential commercial applications due to its good optical properties.1-2 Ce3+-doped YAG phosphor (Ce3+-YAG), combined with blue light emitting diode (LED), is widely used for the white solid state LED.
There are several methods to synthesize YAG particles. For example, the conventional solid-state reaction2-4 is a fairly simple process, but it typically requires high temperature (>1,600° C.) and long reaction time. Furthermore, the YAG particles produced by this method tend to be larger than about 1 μm. The sol-gel method5-7 makes YAG by direct crystallization from amorphous precursor at a lower temperature (˜700° C.), but it requires a more complicated process and an additional thermal treatment at high temperature (>800° C.). The hydrothermal synthesis8-11 also typically requires both high temperature (>400° C.) and high pressure (>30 MPa) to overcome the supercritical condition of water (Tc=374° C., Pc=22.4 MPa).
The organic solvothermal process12-13 has also been used to synthesize YAG powder at lower temperature and pressure. The YAG powder synthesized by the earlier method consists of the aggregates of irregular grains. Although the later solvothermal process14-18 was capable of making monodispersed spherical YAG powder, it still lacked the ability to synthesize Ce3+-doped YAG phosphor at low temperature. Recently, a glycothermal method18-19 has been developed to synthesize Ce3+-doped YAG Nano-phosphors, and the method incorporates a luminescent cerium center into YAG nanoparticles without post heat treatment at high temperatures. However, the glycothermal process affords little control of the inner pressure, along with low recovery ceramic yield and relatively low internal quantum efficiency (IQE).
The embodiments of present invention are directed to an improved solvothermal method for making inorganic nanoparticles that not only allows the interior pressure to be preset prior to the reaction as well as to be adjusted freely throughout the reaction, but also dramatically simplifies the work-up process with high recovery yield. The present invention also makes nanometer sized YAG particles with high internal quantum efficiency (IQE) value.